The present invention relates to blood pressure measuring equipment.
Blood pressure measuring equipment described in U.S. Pat. No. 3,450,131 comprises a sleeve which is attachable to the arm of a person and which defines an inflatable deformable chamber, a microphone being housed in the sleeve. The chamber is coupled to a pressure sensor which is connected via an analog-digital converter, which can be switched on and off, and a gate circuit with a pressure recording device. The microphone is connected through an amplifier with a logic circuit.
During blood pressure measurement, the sleeve is inflated to a pressure lying above systolic pressure and then slowly vented. In that case, Korotkoff tones are generated in a certain pressure range and converted by the microphone into electrical signals. On the occurrence of each Korotkoff tone signal, the analog-digital converter and the gate circuit are controlled by the logic circuit in such a manner that the instantaneous pressure measured by the pressure sensor is recorded in the pressure recording device. The first recorded pressure value corresponds to systolic pressure and the last recorded pressure value to diastolic pressure.
It is known from the "Handbuch der inneren Medizin", published by G. von Bergman, W. Frey and H. Schwiegk, Vol. 9, "Herz und Kreislauf", 5th Part, 1960, Springer Verlag, and "Arterielle Hochdruckerkrankugen", 1970, by A Sturm Jr. Dr. Dietrich Steinkopff Verlag, that the measured pressure values can include an error depending on the circumference of the arm. Such errors are dependent on the ratio of the width of the sleeve to the circumference of the arm.
According to the two afore-mentioned reference works, the errors in in question could be eliminated if the circumference of the arm is measured and then either a narrower or wider sleeve attached to the arm according to its circumference, or else a measured pressure value corrected in dependence on the measured circumference by means of a previously determined correction table or formula.
These correction methods have the disadvantage that the person carrying out the blood pressure measurement must determine the circumference of the arm by a separate measurement and then either select and attach one of several available sleeves or else subsequently perform a correcting calculation. These methods are thus time-consuming as well as complicated, and therefore not suitable in practice.